The U.S. Justice Department has closed a formal antitrust investigation into the U.S. seed industry, which is led by crop biotechnology giant Monsanto Co., without pursuing charges, the government said Friday. [...] The Justice Department, along with the Department of Agriculture, conducted a series of workshops around the country in 2010 examining concentration in the seed, livestock, poultry and dairy markets. The highly-publicized workshops did not result in any major regulatory changes, and Christine Varney, who was the head of the Justice Department's antitrust enforcement at the time, has since left for the private sector.